I always agree with the varied diet approach.
But if I read that an animal eats fruit in the wild, I will at least try to include that. If the animal likes it AND it doesn't cause stomach upset, then I'll keep on until I read otherwise. If an animal is a fruit/greens/bug eater, it would be violating the "varied diet" rules to not include these items in a reasonable ratio. Also the animals seem stimulated by different foods. My bearded dragon will eat his greens, but he goes bonkers for hopping crickets. My russians will faithfully consume clover and endive, but will sprint for a dandelion flower.
When I got my CB K. belliana, the info I found indicated that they were full omnivores who lived in a semi-humid environment. I created the setup and gave it greens/fruit/bugs. It produced solid poops, was active and healthy, and grew nicely with a smooth shell. I considered that a success.
I also had a Vietnamese leaf turtle. I found all varieties of recommendations for these guys. Warm, cool, carnivore, omnivore. It only ate bugs and it would rarely come out from under the substrate, no matter how I varied the environment or diet. I considered that a failure.
Animals don't always eat what the caresheet says. My Russians eat a lot of grass even though they shouldn't. My leopards avoided grass, even though they are supposed to be big grass eaters. Their dietary preference was weeds and greens, which led to runny stools. I compensated with high fiber pellets (Mazuri or Pretty Pets). They had better poop, and grew slowly and evenly.
I think animals might have an instinctual sense for what to eat in their environment, but if you take them out of that environment then they just become opportunistic out of deseperation. Then you get all of those horror stories from the Tortoise Trust about Testudos eating ham and chocolate. My Russians love to chew on my shoes with the orange stripe. I think all they know is "bite brightly colored objects."
I haven't included shoe in the diet.
Yet.